The present invention relates to a control system for a vehicle having an engine and a continuously variable transmission.
As a conventional control system for a continuously variable transmission, there is, for example, one as disclosed in Laid-Open Japanese Patent Application 57-90450 entitled "CONTROL SYSTEM FOR VEHICULAR AUTOMATIC TRANSMISSION." In this conventional control system, a desired reduction ratio is determined from a predetermined optimum reduction ratio characteristic which is predetermined based on a running load, an engine speed and a vehicle speed, and then the reduction ratio in the continuously variable transmission is controlled so as to establish this desired reduction ratio. However, according to this control system, the vehicle is likely to spin and plunge into a dangerous state if the driver depresses the accelerator pedal rapidly to its full stroke in a certain running state because the engine produces its full power output irrespective of the vehicle speed. Another problem stems from the fact that the response in shifting the reduction ratio in the continuously variable transmission to a change in the desired reduction ratio is slow as compared to the response of the engine to a change in throttle opening degree that indicates running load. As a result, the operating state of the vehicle deviates from the optimum reduction ratio characteristic by an amount corresponding to the shifting delay while the throttle opening degree is changing. Therefore, the operating state of the engine can not be controlled desired.